The last time Jeremy had a physical exam, his doctor listened to his heart once — and then he listened to it some more. At the end of the appointment, the doctor told Jeremy and his mom that he heard a heart murmur. Jeremy had to visit another doctor, who listened to his heart again and said that he had a condition called an atrial septal defect. What is it? Why does Jeremy have it? And what needs to be done about it?

What Is an Atrial Septal Defect?

Atrial septal defect (say: AY-tree-ul SEP-tul DEE-fekt), or ASD for short, is a heart condition that can affect kids. To understand an ASD, it helps to know how the heart works:

The heart has four chambers. The lower chambers of the heart are called the ventricles. There are two ventricles: a left ventricle and a right ventricle. The upper chambers are the atria and there are two of them — a left atrium and a right atrium. (Atrium is an old word that meant the main room in an ancient Roman house, so the atria are "rooms" in your heart!)

You may already know that your heart is a muscle that pumps blood throughout your body. In a person without a heart defect, blue blood that's low in oxygen flows first to the right atrium, then to the right ventricle, and is then pumped to the lungs to receive oxygen.

The red oxygen-rich blood then returns to the left atrium, flows from there into the left ventricle, and heads out to the body through the aorta, a large blood vessel that carries blood from the heart to the smaller blood vessels in the body.

Between the right and left atria is a wall called the septum that normally separates the blue and red blood. In a person with an atrial septal defect, there's an opening in that wall. This hole in the wall lets oxygen-rich blood from the left atrium mix with oxygen-poor blood on the other side. The extra blood that ends up crossing through the hole and flowing through the heart and out to the lungs changes the normal "lub-dub" sounds the heart makes and causes an extra swishing sound, which is called a heart murmur. These sounds may be the only clue that a kid has an ASD.

Many kids with an ASD don't have any problems or symptoms because of it. Occasionally, a kid with a very large ASD might have a poor appetite, may tire easily, may grow slowly, can experience shortness of breath, or have lung problems, like pneumonia.

ASD Is a Common Heart Defect

About 1 in every 100 babies is born with some type of heart defect. Atrial septal defects are one of the more common types of these heart defects. A person could be diagnosed with an ASD in infancy, childhood, during the teen years, or even as an adult.

In some kids with small-sized atrial septal defects (small-size holes), the hole can close up on its own. Most kids with a medium-sized or large-sized ASD will need some kind of procedure to close the hole. If the hole is left open, later in life that person may develop other kinds of heart problems, such as an abnormal heartbeat. The person also could develop serious damage to the lung blood vessels. The risk of having a stroke (a problem where a clot or air bubble clogs up a blood vessel in the brain) is also increased in someone with an ASD. To prevent these problems, doctors often recommend closing the hole while the kid is still young.

What Causes an ASD?

Atrial septal defects develop when a baby is still growing inside its mother. Before birth, the heart begins as a large tube that folds and divides into sections that will eventually become the walls and chambers of the baby's heart. If a problem occurs during this process, a hole may develop in the wall between the left atrium and right atrium.

In some cases, the tendency to develop an ASD may be inherited, or genetic. In other cases, an ASD might happen if the pregnant woman was exposed to chemicals or drugs while the baby was growing in her uterus. For most kids with ASDs, no one knows why they developed this problem.

What Do Doctors Do?

Kids who have ASDs may first find out that they have a heart murmur when examined by their regular doctor. The next stop is usually to a pediatric cardiologist (say: pee-dee-AT-rik car-dee-OL-uh-jist), a doctor who specializes in diagnosing and treating heart disease in kids and teens.

The pediatric cardiologist will ask about the kid's medical history (the mother's health during pregnancy and illnesses the kid has had). The cardiologist also will do an exam and listen to the kid's heart. If a doctor thinks a kid may have an ASD, these tests (which don't hurt) might be done:

chest X-ray, which produces a picture of the outline of the heart and surrounding organs in the chest

electrocardiogram, or EKG for short, which records the electrical activity of the heart

echocardiogram (echo), which uses sound waves to create a picture of the inside of the heart

In some kids, the doctor may recommend regular follow-up visits to see if a small defect will close on its own. A kid with a small ASD usually can participate in sports and other regular activities without restrictions.

What if the Hole Doesn't Close?

If the hole needs to be closed, the doctor will decide whether the kid needs surgery or a cardiac catheterization (say: KAR-dee-ak ka-thuh-tur-ih-ZAY-shun). With either one, the kid will get special medicine called anesthesia that causes sleepiness and prevents pain during the operation.

In ASD surgery, the doctor repairs the hole with stitches or a patch made out of either surgical material or the body's own tissue. A kid may have to spend a few days in the hospital after surgery. Within about 6 months, the tissue of the heart heals over the patch or stitches.

Another way to fix the hole is cardiac catheterization. This method uses a thin, flexible tube called a catheter. The cardiologist inserts the catheter into a blood vessel in the leg that leads to the heart. The cardiologist then guides the tube into the heart and inserts a device that covers the hole in the heart. The device is made out of metal mesh and is springy and flexible. The kid usually will spend a night at the hospital after the procedure. As with surgery, over time the heart's natural tissue will grow to completely cover the device.

Kids who have had surgery or cardiac catheterization will need to follow their doctors' instructions about taking it easy for a while. But after just a few weeks, kids can return to their normal activities. Kids with ASDs rarely have any further heart problems. Then ASD can stand for something else: awesome, super, and dazzling!